Soil amelioration by arbuscular mycorrhizal fungi: glomalin production by geographically different isolates of two Glomus species

Arbuscular mycorrhizal (AM) fungi are mutualistic symbionts living in association with the roots of about 80% of land plants. They are key organisms of the soil/plant system, fundamental for soil fertility and plant nutrition. Their host plants obtain mineral nutrients by the large absorbing network of fungal hyphae which spread from mycorrhizal roots into the surrounding soil, thus providing an extensive surface area for water and nutrient absorption. Such extraradical hyphal network plays also an important role in soil quality since it may extend as much as 54 m/g soil and may produce high quantities of glomalin, a protein improving soil structure and stability of aggregates. In this work we assessed the change in glomalin content and the new formation of water-stable aggregates (WSA1-2mm) in an agricultural soil after 4 months’ growth of mycorrhizal and non-mycorrhizal Medicago sativa. We found significant increases in glomalin content and WSA in mycorrhizal pots and differences in glomalin production between isolates of the two species Glomus mosseae and Glomus intraradices. Our findings confirm soil amelioration ability of AM fungi and show the feasibility of screening and selecting AM fungal isolates on the basis of glomalin production. Highly efficient endophytes may represent an useful tool in restoration and revegetation of disturbed soils